Assessment of groundwater vulnerability based on the modified DRASTIC model: a case study in Baicheng City, China

Abstract

Accurate assessment of groundwater vulnerability objectively reflects an area’s potential for groundwater pollution and provides a reference basis for pollution control and prevention. The main objective of this study was to modify the original DRASTIC model to improve the consistency of groundwater vulnerability assessment results with regard to the actual conditions of the study area. To optimize the assessment objectivity, two additional factors that are influenced by human activities (land use and degree of groundwater extraction) were added to form the DRASTICLE model. Then, based on the correlation between all factors and measured nitrate concentrations, the improved three-scale analytic hierarchy process (AHP) and the weights of evidence (WOE) methods were used to reassign the factor weights of the DRASTICLE model. The area under the receiver operating characteristic (ROC) curve, denoted as AUC, was used to quantitatively evaluate the accuracy of all four models (original DRASTIC model AUC: 0.62). By modifying the factors and weights, the three new models showed better performance, AUC values were 0.64, 0.73 and 0.85 for the DRASTICLE, AHP-DRASTICLE, and WOE-DRASTICLE models, respectively. These results indicate that the modified models could more accurately convey groundwater vulnerability in the study area. The WOE-DRASTICLE model, which had the best performance, was then used to assess groundwater vulnerability in 2000 and 2010 and these were compared to 2018. In 2000, 2010, and 2018, the proportion of areas with very high groundwater vulnerability was 5%, 6%, 8%, respectively. Meanwhile, the proportion of areas with very low vulnerability decreased from 73 to 75%, and then rose to 82%, indicating that the spatial distribution of groundwater vulnerability has changed over time. Findings of this study are expected to provide a new theoretical basis for the Baicheng City municipal government in China to better manage and exploit groundwater resources.